The covering power of silver halide emulsions is emulsion manufacturers' great concern because the use of an emulsion having a high covering power enables them to save the amount of silver required to attain a desired optical density. It is disclosed in U.S. Pat. Nos. 2,996,382, 3,178,282, 3,397,987, and 3,607,278, and British Pat. No. 1,426,277 that a remarkably high covering power of silver halide emulsion can be obtained by mixing a surface photosensitive emulsion having a high iodine content with an emulsion comprising small size internally fogged particles. It is further disclosed in Japanese Patent Publication No. 27065/69 (corresponding to U.S. Pat. No. 3,397,987) that the photosensitivity can be increased by adding a polyoxyethylene compound to a silver halide emulsion layer having the above composition.
The inventors have observed that when the abovedescribed polyoxyethylene compound is added to a silver halide emulsion layer comprising a surface photosensitive emulsion and an emulsion of internally fogged particles, the developing speed and the covering power of developed silver are increased. However, the photographic material thus prepared is disadvantageous in that when developed by means of a roller type automatic developing apparatus, it is susceptible to pressure-blackening (hereinafter referred to as "roller mark") by rollers. It is also disadvantageous in that when the above disclosed polyoxyethylene compound is used in a relatively large amount to lower the surface resistivity and improve the antistatic properties of the photographic material, its susceptibility to roller marks is further aggravated. In short, it has not so far been possible for anti-roller mark properties and the antistatic properties to be improved at the same time.